The measurement of temperatures for monitoring and regulating in greatly varying applications is performed, for example, using ceramic hot conductor thermistor elements (“negative temperature coefficient thermistors” or “NTC thermistors”), silicon temperature sensors (for example, so-called KTY temperature sensors), platinum temperature sensors (“platinum resistance temperature detectors” or “PRTDs”), or thermocouples (“TCs”). For sufficient mechanical stability, for protection against external influences, and to avoid corrosion by aggressive media and to avoid temperature-related material changes due to the gas atmosphere in an NTC material or in an electrode, ceramic sensor elements are typically provided with a coating made of a polymer or a glass. The maximum usage temperatures of such sensor elements are limited in the case of a polymer shell to approximately 200° C. and in the case of a glass shell to approximately 500° C. to 700° C.
The described sensor elements cannot readily be used continuously for measuring very high temperatures and/or in particularly aggressive media, however. To nonetheless be able to use them in aggressive media, the sensor elements are often installed in a plastic or stainless steel housings. To produce a thermal contact to the element, potting materials are additionally very frequently used. A significant disadvantage of the systems thus constructed is the delayed response time thereof because of the additional structure-related heat transfers and the low heat conduction of the materials used.
To achieve the lowest possible resistance tolerance of the sensor elements, during the production thereof, the resistance can be readjusted, before the sensor elements are enveloped, by mechanical machining, for example, by trimming, by grinding, or, in the case of glass-enveloped sensor elements, by tempering. A readjustment of the resistance of already enveloped sensors is only possible to a limited extent, however.